This invention relates to improvements in the electrodeposition of zinc from aqueous alkaline cyanide zinc plating baths. More particularly, the improvement relates to a new composition which is particularly suitable as a brightener additive for aqueous alkaline cyanide zinc electrodepositing baths.
Considerable attention has been directed to the development of zinc electroplating baths which will produce zinc deposits of improved quality. Research has been devoted to improving the over-all brightness, the range of allowable current densities, and the ductility of the zinc coatings. Many of the successful aqueous alkaline zinc plating baths contain various quantities of sodium cyanide and various brightener compositions to improve the brightness of the zinc deposits.
Although considerable research has been conducted to develop alkaline plating baths which do not contain cyanides, there continues to be a demand for alkaline systems which do contain cyanide ions and which produce desirable zinc deposits. In general, the alkaline cyanide baths are less expensive to operate. One reason for the reduced expense is that the alkaline cyanide baths consume lesser amounts of additives such as brighteners when compared to non-cyanide plating baths. Moreover, alkaline cyanide zinc plating baths generally are more effective in plating substrates having recesses (such as cup shapes).
Blends of polyvinyl alcohol with other active brightening ingredients have been disclosed as being useful in alkaline cyanide zinc plating baths in, for example, U.S. Pat. Nos. 3,318,787 and 3,411,996. Aqueous alkaline zinc electroplating baths containing vinyl alcohol polymers and copolymers degraded with periodic acid or an alkali metal periodate have been described in U.S. Pat. No. 3,769,183. These baths are reported to give improved plating characteristics at low applied currents.
The use of bath soluble polyethyleneimines as addition agents in alkaline zinc cyanide electroplating baths has been described in U.S. Pat. No. 3,393,135. In U.S. Pat. No. 4,146,442, the use of polymeric nitrogen-containing compounds prepared by reacting poly(alkyleneimines) with a cyclic carbonate have been described.